An electric discharge machine is arranged to perform electric discharge machining, with a workpiece immersed in machining fluid filled in an electric discharge machining tank, or while jetting the machining fluid from a nozzle toward the workpiece. In the case of machining the workpiece immersed in the machining fluid, it is undesirable if an upper wire guide or the like is immersed in the machining fluid, or if the upper part of the workpiece is exposed above the machining fluid level. Conventionally, therefore, an opening which extends vertically is formed in the peripheral wall of the electric discharge machining tank, and a fluid level adjusting plate is attached to the opening-formed portion of the peripheral wall of the machining tank in a manner vertically slidable relative to the peripheral wall, so as to make it possible to manually adjust the height of the top edge of the plate for adjustment of the fluid level in accordance with the workpiece thickness.
However, according to the aforementioned conventional fluid level adjusting device, it takes time to manually adjust the height of the top edge of the fluid level adjusting plate. Also, it is difficult to maintain the watertightness between the fluid level adjusting plate and the peripheral wall of the machining tank, and hence machining fluid tends to leak through a gap between the peripheral wall and the plate. For this reason, conventionally, in order to compensate for the leakage of the machining fluid, a machining fluid supplying pump is driven to discharge a little more volume of machining fluid than actually required, thus causing the machining fluid to overflow at all times. Therefore, the fluid level must be adjusted in dependence on the leakage of the machining fluid so as to assure proper overflow. This makes it difficult to accurately adjust the fluid level. In addition, extra energy is wasted for driving the pump, leading to a shortened service life of the pump.